The Herculoids were a group of heroes who lived on the planet Amzot. Zandor, the patriarch, possessed formidable fighting skills and employed a slingshot to fire energy rocks at foes. His wife Tara and son Dorno functioned in supporting roles - occasionally getting kidnapped by the episode's villain, and occasionally helping to save the day. Far more dangerous were the special animals Zandor called friends: Igoo, a monstrous stone giant of immense strength but limited wit, Zok, a flying dragon that could emit energy beams from its eyes and tail, and Tundro, a vaguely rhinoceros-like creature with thick armor and the ability to launch exploding missiles from its hollow horn. Although not as strong as Igoo, it could also bring plenty of muscle to bear. Rounding out the crew were Gleep and Gloop. These blobs sported only a pair of black eyes each, and could reshape their bodies in many ways, sometimes even dividing into independent units and recombining later.

The Herculoids needed all this power, for the list of villains who invaded Amzot was long and varied: androids, laser lancers, spider creatures, aliens of all sorts, menaces from the planet itself - week in and week out, Zandor found himself hard pressed to fend them off, but always and ultimately did so with help from his family and his stable of friendly creatures.